Rubber composition and pneumatic tire using the same

Abstract

There is provided a rubber composition exhibiting excellent storage modulus and loss factor without damaging the operability. The rubber composition is characterized by containing 5-60 parts by mass of an aromatic vinyl compound-diene compound copolymer (B) having a weight average molecular weight of 5,000-300,000 (conversion to polystyrene through gel permeation chromatography) based on 100 parts by mass of a rubber component comprising at least one rubber of natural rubber and synthetic diene-based rubbers in which the copolymer (B) comprises 5-80 mass % of the aromatic vinyl compound and a vinyl bond content in diene compound portion is 10-80 mass %. This rubber composition can be used in a tread compounding for a tread portion.

1 . A rubber composition characterized by containing 5-60 parts by mass of an aromatic vinyl compound-diene compound copolymer (B) having a weight average molecular weight of 5,000-300,000 (conversion to polystyrene through gel permeation chromatography) based on 100 parts by mass of a rubber component comprising at least one rubber of natural rubber and synthetic diene-based rubbers in which the copolymer (B) comprises 5-80 mass % of the aromatic vinyl compound and a vinyl bond content in diene compound portion is 10-80 mass %.  
   
   
       2 . A rubber composition according to  claim 1 , wherein the rubber component (A) comprises not less than 50 mass % of a styrene-butadiene copolymer rubber.  
   
   
       3 . A rubber composition according to  claim 1 , wherein the rubber component (A) contains not less than 50 mass % of a styrene-butadiene copolymer (C) having a weight average molecular weight of 300,000-1,500,000, and the copolymer (C) comprises 20-60 mass % of an aromatic vinyl compound and has a vinyl bond content in diene compound portion of 10-80 mass %, and the copolymer (B) comprises 10-70 mass % of an aromatic vinyl compound, and a difference in aromatic vinyl compound content between the copolymer (C) and the copolymer (B) is not more than 30 mass %.  
   
   
       4 . A rubber composition according to  claim 3 , wherein the copolymer (C) is at least one of an emulsion-polymerized styrene-butadiene copolymer comprising not less than 20 mass % of an aromatic vinyl compound and a solution-polymerized styrene-butadiene copolymer comprising not less than 20 mass % of an aromatic vinyl compound and having a vinyl bond content in diene compound portion of not less than 10 mass %.  
   
   
       5 . A rubber composition according to  claim 1 , wherein the aromatic vinyl compound of the copolymer (B) is styrene.  
   
   
       6 . A rubber composition according to  claim 1 , wherein the diene compound of the copolymer (B) is butadiene.  
   
   
       7 . A rubber composition according to  claim 1 , wherein the copolymer (B) is a solution-polymerized styrene-butadiene copolymer rubber.  
   
   
       8 . A rubber composition according to  claim 1 , wherein the copolymer (B) has a weight average molecular weight of 20,000-200,000.  
   
   
       9 . A rubber composition according to  claim 1 , wherein the copolymer has a weight average molecular weight of 50,000-150,000.  
   
   
       10 . A rubber composition according to  claim 1 , which further contains 30-90 parts by mass of a filler based on 100 parts by mass of the rubber component (A).  
   
   
       11 . A rubber composition according to  claim 10 , wherein the filler is at least one of carbon black and silica.  
   
   
       12 . A rubber composition according to  claim 11 , wherein the carbon black is SAF class to HAF class.  
   
   
       13 . A rubber composition according to  claim 1 , wherein a total amount of the copolymer (B) and a softening agent is 5-80 parts by mass based on 100 parts by mass of the rubber component (A).  
   
   
       14 . A rubber composition according to  claim 1 , wherein a total amount of the copolymer (B) and a softening agent is 5-60 parts by mass based on 100 parts by amass of the rubber component (A).  
   
   
       15 . A pneumatic tire characterized by using a rubber composition as claimed in  claim 1  in at least ground contact part of a tread portion.